<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    //ES6 新增了let命令，用来声明变量。它的用法类似于var，但是所声明的变量，只在let命令所在的代码块内有效。
    {
      let a = 10;
      var b = 1;
    }
    //console.log(a);// ReferenceError: a is not defined.
    console.log(b);// 1

    //for循环的计数器，就很合适使用let命令。
    for (let i = 0; i < 10; i++) {
      // ...
    }
    console.log(i);// ReferenceError: i is not defined
  </script>
</body>

</html>